Electromagnetic waves are radiated from cables of electric appliances and electronic appliances, and ambient electromagnetic waves intrude into cables, so that noises enter signals. To prevent the radiation and intrusion of electromagnetic waves to and from cables, cables are conventionally shielded with metal nets or foils. For example, JP 11-185542 A discloses a cable having a thin magnetic shield film, which comprises an insulating tape wound around pluralities of signal-transmitting cables, a laminate tape of a high-conductivity metal foil (copper foil, etc.) and a thin film of a high-permeability material (permalloy, etc.) wound around the insulating tape, and an insulator wound around the laminate tape. However, it fails to achieve complete shielding for high-frequency noises. Accordingly, it is proposed to prevent the radiation and intrusion of electromagnetic waves by absorption instead of shielding.
JP 2005-259385 A discloses a communications cable comprising pluralities of first pair-conductor cables each comprising two metal wires electrically insulated with a rubber sheath, a first sheath covering the first pair-conductor cables, pluralities of second pair-conductor cables each comprising two metal wires electrically insulated with a rubber sheath, a second sheath covering the second pair-conductor cables, a metal net outside the second sheath, and an insulator layer. Each of the first and second sheaths has a two-layer structure comprising a magnetic layer and a conductor layer. The magnetic layer is formed by, for example, a sheet comprising fine amorphous alloy particles bonded by a binder, and the conductor layer is formed by, for example, a sheet comprising fine silver particles bonded by a binder. However, because the sheath having a two-layer structure comprising a magnetic layer and a conductor layer is used in this communications cable, the cable is inevitably thick and expensive.
JP 2009-71266 A discloses a communications cable having a structure comprising a signal-conducting wire or power-conducting wire covered with an insulating layer, an electromagnetic-wave-absorbing/shielding film comprising an electromagnetic-wave-shielding layer and an electromagnetic-wave-absorbing layer being wound around the cable in the insulating layer. An exemplified electromagnetic-wave-shielding layer is an electromagnetic-wave-shielding film as thick as 17-70 μm, which is constituted by a polymer film laminated with an aluminum or copper foil or vapor-deposited with Al or Cu. An exemplified electromagnetic-wave-absorbing layer is an electromagnetic-wave-absorbing film as thick as 10-100 μm, which is coated with a paint containing metal flake and/or electromagnetic-wave-absorbing Fe—Si alloy powder, Fe—Si—Cr alloy powder, amorphous metal powder, etc. However, because the electromagnetic-wave-absorbing/shielding film has a two-layer structure comprising the electromagnetic-wave-shielding layer and the electromagnetic-wave-absorbing layer both relatively thick, the communications cable is inevitably thick and expensive.
Because the cables are likely arranged in electric appliances and electronic appliances having complicated structures, they are preferably as thin as possible. However, with a structure having both electromagnetic-wave-shielding layer and electromagnetic-wave-absorbing layer as in the above conventional technology, it is difficult to make the cable thinner. In addition, the two-layer structure of an electromagnetic-wave-shielding layer and an electromagnetic-wave-absorbing layer makes the cable expensive.